Not only is Judaism a religion of love. It was the first civilisation to place love at the centre of the moral life. C. S. Lewis and others pointed out that all great civilisations contain something like the golden rule: Act toward others as you would wish them to act toward you, or in Hillel’s negative formulation: Don’t do to others what you would hate them to do to you. This is what games theorists call reciprocal altruism or Tit-for-tat. Some form of this (especially the variant devised by Martin Nowak of Harvard called “generous”) has been proven by computer simulation to be the best strategy for the survival of any group.